inter-rivet buckling width

[RichardHurwitz]

thread2-110541

The sugesstion to use 2b (where b is the rivet spacing) for the effective width is an excellent one, but do not use this width with the standard inter-rivet buckling stress found in various sources such as Bruhn. I think the difference is about 18% with Timoshenko being higher.

It should be used with the following expression from Timoshenko Theory of Elastic Stablity for a concentrated point buckling load on a panel. 2b is within 2.7% of a infinitely wide sheet so if your sheet is not continuous an adjustment might need to be made. If e/D=2 I think the expression is ok. If less the stress and effective width and hence load will be less.

Pcr = 4 * pi * D / b ALL FOUR(4) EDGES SIMPLY SUPPORTED

Pcr = 8 * pi * D / b ALL FOUR(4) EDGES SS and fixed in rotation

The supports on the left and tight reall don't matter since they are an infinite distance away from the rivet centerline. The support at the top and bottom represent whether the user thing the edge is SS or fixed. The fixed solution is similar to Fcr = 3E/(L/rho)^2

where pi = 3.14159 etc.

D = E * t^3 / [12 * ( 1 - nu^2)

where E = Ec = Young's moduls in compression
t = thickness
nu = Poisson's ratio

 

[RichardHurwitz]

I made an FEM model which checked well with SS but not clamped.

The ratio between the two methods is ~3 not 1.18

Only two edges - top and bottom are clamped.

I'mm not to happy with the results.

 

[rb1957]

without thinking about it i would have used 30t

 

[RichardHurwitz]

I think I am prepared to answer the question of what effective width to use for inter-rivet buckling in order to calculate the load the skin is carrying when the skin buckles.

Fir must be less than or equal to Fcy

From Bruhn on page C7.10 equation C7.15 for a continuous sheet reads

w1 = 1.7 * t * (Ec/Fir)^0.5

where 1.7 has been substituted for 1.9 (see page C7.11 “experiments”) and Fir has been substituted for Fcy.

The load carried by the skin is given by

Load = w1 * t * Fir

From Bruhn on page C7.11 equation C7.15 reads

w2 = 0.62 * t * (Ec/Fir)^0.5

Make sure that you limit w2 to the actual edge distance (e).

where Fir has been substituted for Fcy.

The load carried by the skin is given by

Load = (w1/2 +w2) * t * Fir